The present invention relates to prills of nitrogen-containing salts having enhanced structural integrity or thermal stability. More particularly, nitrogen-containing salts such as ammonium nitrate are treated with an aminosulfonate product to impart hardness anti-caking and anti-dusting properties to the salt particles without affecting the end use properties of the salt.
Nitrogen-containing salts such as ammonium phosphates, ammonium nitrates, potassium nitrates, and many others are well known as components for fertilizers and explosive compositions. Methods of manufacturing these nitrogen-containing salts as well as methods of processing the nitrogen-containing salts into particles via prill and/or granulation techniques are also well known. The resulting nitrogen-containing salt particles, however, exhibit certain undesirable characteristics. Such particles tend to cake when stored and transported in bulk such that the initial free flowing particles change to a solid, substantially integral mass. Secondly, such particles easily break into smaller particles resulting in a substantial amount of dust being created when handled or transported or when, if used as a fertilizer, eventually applied to the soil. Hardness is important for both explosive and fertilizer applications. In explosive applications it is difficult to achieve the competing goals of porosity and hardness. In fertilizer applications, particle porosity is not particularly important and can be undesirable, but hardness remains important for the reasons outlined above.
In order to overcome the above disadvantages, the prior art has taught a number of conditioning agents which may be added to the nitrogen-containing salt during processing to harden and give anti-caking and anti-dusting properties to the nitrogen-containing salt particles. For example, anti-caking properties have been imparted to nitrogen-containing salt particles by utilizing clay, talc, surfactants, or a combination of these three conditioners, to coat the particles. Additionally, various oils can be sprayed on the particles for controlling dust. Also, a phosphoric acid-boric acid compound known under the trademark “Permalene” and available from Mississippi Chemical, has been utilized in phosphate production as a hardening agent.
European Patent Application 569 118, Nov. 10, 1993 discloses hardening ammonium nitrate prills and granules by combining ammonium nitrate with a functionally active polymer having a molecular weight of 200 to 700,000. The functionally active groups on the polymer can be ionic species such as sulfonates; examples are polystyrene sulfonate and polystyrene sulfonate co-polymerized with maleic anhydride, or, in another example, polyvinyl sulfonate. One embodiment is presented by the formula where Y is a connecting group which may be a hydrocarbon of up to 8 carbons.
U.S. Pat. No. 5,597,977, Chattopadhyay, Jan. 28, 1997, discloses hardening ammonium nitrate by combining it with a functionally active polymer such as polystyrenesulfonate or polyvinylsulfonate.
The present invention, therefore, solves the problem of providing prills and other particles of nitrogen-containing salts with improved properties, by adding thereto an aminosulfonate or condensation product thereof, as described in greater detail hereinafter. The addition of aminosulfonate or condensation product to the inorganic nitrogen-containing salts generally results in harder particles less susceptible to breakage and formation of fines, and/or provides anti-caking and anti-dusting properties in one step without the need for any secondary or additional conditioners.